Barge arrangements comprising a barge adapted to take cargo and without propulsion power and a tug with propulsion power are generally known. Such barge arrangements often include a propelling tug deployed for several barges. The arrangement is operated by loading/unloading one barge at port while another barge is propelled at sea. This means that the tug with its machinery and crew are in efficient use at sea, whereby less non-productive time is spent in port. Typically such barge arrangements are pusher-barge combinations, where the tug engages the stern of the barge for pushing the barge bow forward. Examples of known barge arrangements are shown e.g. in GB 2 132 566 A and U.S. Pat. No. 4,356,784.
The cited barge arrangements are of an integrated tug-barge (ITB) type, where the tug and barge are locked together in a rigid connection practically forming one unit, whereby there is no movement between the tug and barge. The barge arrangement can also be an articulated tug-barge (ATB) type, where the tug and barge have an articulated or hinged connection, which allows for relative movement in one axis or plane for fore (bow) and aft (stern) pitch.
Normally the known pusher-barge combinations are designed for operation in open sea, whereby conventional ice-breakers are used for assistance for operation in ice conditions.
In an attempt to obtain a multi-purpose ship a so-called double acting ship (DAS) has been developed. In this known ship the bow is a conventional bow for operation in open sea and the stern is designed for ice-breaking purposes and provided with a turnable screw arrangement, e.g. azimuthing pod propulsion. When operating in open sea the ship moves with the bow in a forward direction and when operating in ice conditions the ship moves with the ice-breaking stern in the forward direction. As the propulsion system is turnable, the propeller(s) can be used to flush the ship's hull in order to reduce ice friction. The solution is disclosed e.g. in U.S. Pat. No. 5,218,917. This solution, however, is very expensive in construction and operation. The ship practically has to constructed as an ice-breaker, whereby also the ice-breaking stern is not suitable as a stern for operation in open sea due to its ice-breaking configuration. In addition, crew and machinery are idle in port, as opposed to the known barge arrangement discussed above.